The present invention relates to liquid crystal compositions and, more particularly, to novel liquid crystal compositions having a terphenyl constituent mixed with a four-part cyclohexane constituent.
Use of liquid crystal displays is desirable, due in part, to the relatively low operating power consumption thereof. Typical liquid crystal materials for use in such displays, and typically utilized as a host material for a guest dichroic dye in dichroic liquid crystal displays, have generally been unable to provide a working temperature range from a melting point of less than 0.degree. C. to a clearing point (the nematic-to-isotropic transition temperature) of greater than 85.degree. C. In many applications, this extended temperature range of 0.degree. C. to +85.degree. C. is required. For example, commercially available liquid crystals of the biphenyl type, found to be useful for display devices due to relatively good stability and electro-optic behavior, may be eutectic mixtures, such as are sold under the designations E-7 and E-8 by BDH Chemicals, of Great Britain; the nematic range of the E-7 mixture is about 0.degree. C. to about +60.degree. C., whereas the nematic range of the E-8 mixture is about -10.degree. C. to about + 70.degree. C. A eutectic mixture of three phenylcyclohexanes and one biphenylcyclohexane, commercially available as Merck 1132, from EM Laboratories, Darmstadt, West Germany, has a nematic range of -6.degree. C. to +70.degree. C. It is known that the operating temperature range of a liquid crystal composition may be broadened by adding another liquid crystal material which has a very high nematic-to-isotropic transition temperature material will raise the nematic-to-isotropic transisition temperature of the mixture, but, depending upon the interaction of the additive with the molecules of the original liquid crystal composition, the melting temperature (crystal-to-nematic transition temperature) may be increased and an incompatibility between the original and additive liquid crystal compositions may be found. There is, therefore, a very delicate balance of lateral and intermolecular attractions between molecules which allows a liquid crystal mixture to have a broad nematic range, while possessing stable structures, and which results are presently incapable of precise prediction when original and additive liquid crystal materials are mixed together to form a liquid crystal composition having a desired nematic temperature range.